The invention relates to a digital recording and reproducing system. The system comprises a device for recording a digital electric signal in a longitudinal track on a record carrier and a device for reproducing the digital electric signal from the track on the record carrier. The recording device has an input for receiving the digital electric signal with a specific sample rate and is adapted to convert the applied digital electric signal into a form in which it can be accommodated in consecutive frames at a specific bit rate, which frames can be recorded in the track on the record carrier. The reproducing device is adapted to read the frames from the track on the record carrier, to decode the information contained in the frames into a digital electric signal having substantially the same sample rate and to supply that digital electric signal to an output. The invention also relates to a recording device and a reproducing device for use in the digital recording and reproducing system, and to a record carrier obtained by means of the recording and reproducing system in accordance with the invention.
A recording and reproducing system of the type defined in the opening paragraph is known, for example, from the book "The art of digital audio" by J. Watkinson, Focal Press 1988, Chapter 9. Chapter 9.20 of this book describes, for example, a system known as SDAT. In that system a digital audio signal is recorded in a plurality of juxtaposed tracks formed, or to be formed, on a record carrier in the longitudinal direction of the record carrier. The recording device is intended for recording a digital signal, such as a digital audio signal originating from a digital signal source such as a Compact Disc audio player, on the record carrier. For this purpose, the digital signal having a specific sample rate fs, which is fs=44.1 kHz if the digital source is a CD player, is applied to the recording device. In the recording device, the digital electric signal is converted into a form in which it can be recorded on the record carrier. Recording in the track is effected at a bit rate which is neither equal to nor locked to the sample rate fs. For this purpose, the recording device comprises a separate frequency source (crystal). However, a problem may arise because the sample rate at which the digital electric signal is applied to the recording device varies. Moreover, the frequency supplied by the frequency source may vary. The last-mentioned frequency variations may be caused, for example, by temperature fluctuations affecting the frequency source.
The recording device also has an analog input. An analog electric signal applied via this input is sampled at a sample rate of 44.1 kHz and is digitized. In order to enable the analog signal to be sampled at 44.1 kHz, it is generally necessary to have a second frequency source (crystal) to supply the sampling frequency of 44.1 kHz. However, the frequency supplied by the second source may also vary. If the digital signal is to be recorded correctly on the record carrier, the variations in the sample rate and the clock frequency of the first-mentioned frequency source should be allowed and compensated for.
In the prior-art devices, this is realized, inter alia, by loading the samples of the digital signal, which are received with a variable sample rate, into a memory and by reading them out of this memory at a fixed frequency. Moreover, transport speed control is applied to compensate for the variable bit rate with which the signal processor in the recording device supplies the information in the frames for recording on the record carrier.